The present invention relates to the field of medical diagnostic and therapeutic devices in general and to a system for intravascular characterization of blood vessel lesions and vascular bed.
Vascular diseases are often manifested by reduced blood flow due to atherosclerotic occlusion of vessels. For example, occlusion of the coronary arteries supplying blood to the heart muscle is a major cause of heart disease. Numerous methods are currently available for treating various lesion types. Some of these methods are given herein below, sequenced from xe2x80x9csofterxe2x80x9d to xe2x80x9cheavierxe2x80x9d, relating to their ability to open calcified lesions; per cutaneous transluminal angioplasty (PTCA), xe2x80x9cCutting balloonxe2x80x9d angioplasty, directional coronary atherectomy (DCA), rotational coronary atherectomy (RCA), Ultrasonic breaking catheter angioplasty, transluminal extraction catheter (TEC) atherectomy, Rotablator atherectomy, and excimer laser angioplasty (ELCA). Often, stents are placed within the lesion so as to prevent re-closure of the vessel (also known as recoil).
Lesion characteristics, together with vessel condition proximal and distal to the lesion and vascular bed condition are used to determine the medically and economically optimal treatment method or combination of methods of choice. Geometry, pressure and flow are three variables often measured in the cardiovascular system. These measurements are performed prior, during and after the treatment, providing diagnostic and therapeutic data. The measurement prior to the treatment allows careful treatment selection. Measurements during and after the treatment enable evaluation of the treatment efficacy. Recent progress in probe miniaturization opened a whole new range of pressure and flow measurements that have been previously impossible to perform.
Lesion geometry is evaluated by angiography, qualitative coronary angiography (QCA), or by intravascular ultrasound (IVUS). These measurements allow calculation of the percent diameter stenosis (angiography or QCA) or percent area stenosis (IVUS). This information is used to estimate stenosis severity, but during the last years clinicians have realized that direct physical information about pressure and flow is necessary for complete evaluation of coronary artery disease. Physiological measurements such as pressure gradient have been clinically used as an indicator for lesion severity. However, previous attempts to relate the pressure gradient across the stenosis to its functional significance have been disappointing. The decrease in the pressure gradient after PTCA has been used to assess the success of the treatment, with poor correlation.
Other parameters have been defined and proven more effective as indicators for lesion severity. The coronary flow velocity reserve (CFVR) is defined as the ratio of hyperemic to baseline flow velocity. The fractional flow reserve (FFR) is defined as the ratio of distal (to stenosis) pressure (Pd) to aortic pressure (Pa) during hyperemia. Hyperemic conditions are obtained by administration of vasodilators (e.g. papaverine, adenosine). Clinical studies have demonstrated that in most cases, lesions with CFVR less than 2 must be treated using one of the above mentioned methods, whereas for patients with CFVR greater than 2, angioplasty may be avoided. Similarly, in most cases angioplasty may be avoided if FFR greater than 0.75. Coronary flow occurs essentially during diastole while systolic contribution to total coronary flow is smaller. A notable difference between diastolic to systolic velocity ratio (DSVR) was observed between normal and stenotic arteries. A cut-off value of 1.7 was proposed to distinguish between significant and non-significant lesions.
The FFR and CFVR are independent but complementary indicators. The first characterize the specific lesion whereas the second is a more global parameter, characterizing the lesioned vessel (lesion and distal bed). Clinical studies (Di Mario et al., Catherization and Cardiac Diagnosis 38, 189-201, 1996) show that for approximately 75% of the patients CFR and FFR lead to the same conclusion regarding the lesion significance. At the same time, for 25% of the patients, the conclusions regarding lesion significance were different. This means that simultaneous determination of coronary flow reserve and fractional flow reserve is highly important and gives the clinician the additional and more complete information regarding the lesion severity.
Major technical progress has been made lately with respect to pressure and velocity monitoring guide wires. For example, 0.014xe2x80x3 Pressure Wire (trademark) (Radi Medical System, Uppsala, Sweden) is now available for intracoronary pressure measurements. However, for light stenosis, these measurements may be performed using diagnostic low profile catheters, Millar pressure transducer catheters (available by Millar Instruments, Inc., Houston, Tex., U.S.A.) or any other intravascular pressure equipment.
A 0.014xe2x80x3 Doppler Flow wire (Cardiometrics Inc., Mountain View, Calif.) is now available for intracoronary velocity measurements. Both wires may be advanced into distal parts of the coronary tree without significantly impeding the flow. Simultaneous measurements of FFR and CFVR require the use of both wires. Such a procedure is complicated, expensive and was used only for research purposes. Therefore, clinicians use either velocity measurements to calculate coronary flow velocity reserve (CFVR) or pressure measurements to calculate fractional flow reserve (FFR). Furthermore, working with the Flow wire is sensitive to the location of the tip within the vessel cross section. The wire tip will measure accurately if located along the longitudinal axis. However, significant errors will appear once the wire is within the boundary layer. Therefore, manipulating the Flow wire requires high expertise and a lot of experience. Fortunately, these limitations are not relevant to the pressure wire measurements, yielding accurate data with simple handling.
This invention provides a method for calculating the flow-based clinical characteristics, coronary flow reserve (CFR) and diastolic to systolic velocity ratio (DSVR), in addition to the FFR, using pressure measurements across a stenosis. In addition coronary flow reserve in the same vessel without stenosis (CFR0) may be estimated as well as aneurysms. FFR, CFR, CFR0 and DSVR are simultaneously calculated for a complete characterization of the vessel of interest. Further, the present invention relates generally to a sensor apparatus for determination of characteristics in a tubular conduit, such as a blood vessel or the urethra, having at least one pressure sensor adapted to measure pressure across an obstruction.
The invention provided, includes a processor unit operatively connected to the at least one sensor, a program for controlling the processor unit. The processor unit is operative with the program to receive signals from the sensor; identify changes in the sensor signal; detect characteristics of the tubular conduit, the characteristics of the tubular conduit being divided from changes in the sensor signal; and recognized and assign a label to the characteristic of said tubular conduit. This invention provides a system which includes the Automatic Similar Transmission method.
The characteristics that may be determined include a flow ratio in a blood vessel; a coronary flow reserve in a blood vessel; diastole to systole velocity ratio in a blood vessel; coronary flow reserve together with fractional flow reserve in the same blood vessel without stenosis and analysis of their correlation for estimation of vascular bed conditions; coronary flow reserve together with fractional flow reserve in the same blood vessel with out stenosis for estimation of vasodilatation effectiveness.
Further, this invention provides the determination of a hemodynamic condition of the artery by determining the vascular bed index (VBI0) which is equal to the ratio of mean shear to mean pressure. The invention provides a system and methods for determining the vascular bed index.
Further, the present invention provides a methods of determining/detecting microvascular disease due to the abnormal ratio of FFR to CFR based on either or proximal and/or distal pressure. The method may be in combination with a balloon procedure. Also, the methods described provide for post PTCA evaluation (prior to stenting), determination or validation of dilatation success by subsequent CFR increase after PTCA, and indication of whether a stent is neded. The methods and systems provided herein, indicate high probability or microvascular disease, due to the abnormal ratio of FFR to CFR. Further, Post Stenting in combination with a deflation balloon allows the estimation of CFR of the vessel. Thus, in one embodiment of the invention only a distal pressure measurement will allow the CFR calculation.
Lastly, this invention provides determining CFR and FFR directly from intraarterial pressure measurements, thus the simultaneous CFR and FFR measurements permit one to obtain additional information about the vascular bed. The present invention provides the hemodynamical parameters in estimating the severity of stenotic blood vessels in an attempt to increase the reliability of these parameters.